Oxidative Stability Of Edible Oils Research Articles

Prediction of oxidative stability in bulk oils using dielectric constant changes

The effects of amphiphilic compounds on the dielectric constant of bulk oils were determined and the utility of the dielectric constant as a reliable parameter for predicting the oxidative stability of edible oils was evaluated. As the content of monoacylglycerols (MAGs), lecithin, and moisture increased, the dielectric constant of modified corn oil increased at different rates, whereas the addition of free fatty acids, including oleic and linoleic acid, decreased the dielectric constant of modified corn oil. Unoxidized fresh bulk oils showed a wide range of dielectric constants, from 8 for canola oils to 33 for flaxseed oils. The dielectric constant showed a strong correlation with the percentage of unsaturated fatty acids in the bulk oils. Oils with low oxidative stability had a high dielectric constant. Overall, the dielectric constant of bulk oils is strongly correlated with the content of amphiphilic compounds, moisture content, and degree of unsaturation of fatty acids.

Determination of the oxidative stability of olive oil using an integrated system based on dielectric spectroscopy and computer vision

During storage, olive oil may suffer degradation leading to an inferior quality level when purchased and consumed. Oxidative stability is one of the most important parameters for maintaining the quality of olive oil, which affects its acceptability and market value. The current methods of predicting the oxidative stability of edible oils are costly and time-consuming. The aim of the present research is to demonstrate the use of dielectric spectroscopy integrated with computer vision for determining the oxidative stability index (OSI) of olive oil. The most effective features were selected from the extracted dielectric and visual features for each olive oil sample. Three machine learning techniques were employed to process the raw data to develop an oxidative stability prediction algorithm, including artificial neural network (ANN), support vector machine (SVM) and multiple linear regression (MLR). The predictive models showed a great agreement with the results obtained by the Rancimat instrument that was used as a reference method. The best result for modelling the oxidative stability of olive oil was obtained using SVM technique with the R-value of 0.979. It can be concluded that this new approach may be utilized as a perfect replacement for quicker and cheaper assessment of olive oil oxidation.

Effects of olive wastewater and pomace extracts, lecithin, and ascorbyl palmitate on the oxidative stability of refined sunflower oil

In this study, the effects of olive mill wastewater (OMW) and olive pomace (OP) extracts (1 and 2 mg/g), lecithin (L, 1–5 mg/g), and ascorbyl palmitate (AP, 0.2 mg/g) on the oxidative stability of refined sunflower oil (SFO) and its purified triacylglycerols (TAGs) were investigated under accelerated oxidation conditions. Induction period of TAGs increased from 6.84 to 11.27 hr, with OMW methanol extract (1 mg/g), while OP extracts provided less protection (9.79 hr) at 90°C in Rancimat. The K232 values of the SFO with extracts (1 mg/g) and AP (0.2 mg/g) was lower than those of butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and α-tocopherol containing oil samples at 60°C. Binary combinations of extracts with AP (0.2 mg/g) or L (5 mg/g) also effectively decreased the K232 and K270 values of TAGs during oxidation. In conclusion, OMW and OP extracts can be synergistically used with L or AP for stabilization of SFO against oxidation. Practical applications Generally, edible oils contain high amount of unsaturated fatty acids which are susceptible to oxidation during heat required food processes. Natural antioxidants are preferably used for increasing oxidative stability of edible oils. Olive mill byproducts contain valuable phenolic compounds that have high antioxidant capacity. In this study, we studied antioxidant efficiencies of the olive wastewater and pomace extracts in sunflower oil in combinations with lecithin and ascorbyl palmitate. These combinations can be successfully used to increase the oxidative stability of sunflower oil.

Migration Study of Antioxidant in Durian Rind Cellulose Reinforced Poly(Lactic Acid)(PLA) Biocomposites and its Effect on Oxidative Stability of Edible Oil

The migration of antioxidants including α-tocopherol (AT) and butylated hydroxytoluene (BHT) from durian rind cellulose reinforced poly (lactic acid) (PLA) biocomposites into 95% ethanol and its effect on stability of edible oil were investigated. The biocomposites materials containing 5% w/w antioxidant were compounded using Brabender internal mixer followed by hot press machine and were then placed in contact with 95% ethanol at 27°C and 37°C. Released antioxidants were measured by UV-spectroscopy for 45 days. The material containing BHT generated the faster release than α-tocopherol. Both of antioxidants released at 37°C faster than 27°C. The faster release of antioxidant from each condition resulting inhibition of lipid oxidation. Oxidative stability of edible oil was investigated by monitoring of peroxide value (PV) of edible oil. The result was found that edible oil contact with biocompotises containing BHT showed lower PV compared to α-tocopherol during storage. Therefore, it can be summarized that BHT is suitable antioxidant to be used in active packaging application for edible oil.

Thermal and oxidative stability of Sacha Inchi oil and capsules formed with biopolymers analyzed by DSC and 1H NMR

The oxidative stability of edible oils is an important feature to know due the undesirable changes that can occur in the storage. In this way, the oxidative induction time (OIT) value is an indicative to prevent this effect. The objectives of this study were to evaluate the omega-3 content and kinetic parameters of Sacha Inchi oil (SIO) and capsules that are formed with biopolymers, in addition, there were analyzed with differential scanning calorimetry (DSC) and proton nuclear magnetic resonance (1H NMR). The SIO and capsules, formed using an emulsion, were analyzed with DSC in an oxygen atmosphere to determine the OIT value in isothermal conditions at 100, 120 and 150 °C. The kinetic parameters (activation energy, pre-exponential factor and z value) of SIO were obtained, and the stability time was predicted at different temperatures. The 1H NMR spectra enabled us to assess the identification and percentage relative before and after the isothermal DSC oxidation of omega-3 concentration and formation of their oxidized compounds. (E-E)-2,4-Alkadienals were the primary oxidized compound and is strongly correlated with the decrease in omega-3 content. Isothermal DSC is a useful to determine the OIT (min) and kinetic parameters to predict the stability oxidation in different edible oils and thus prevent the inadequate consumption of edible oils oxidized.

Effect of unsaponifiable matter extracted from Pistacia khinjuk fruit oil on the oxidative stability of olive oil.

The present study was carried out to investigate the improvement of oxidative stability of refined olive oil using various concentrations of unsaponifiable matters extracted from Pistacia khinjuk fruit oil (UFO). For further elucidation of UFO antioxidative power, tertbutylhydroquinone (TBHQ) was used in an olive oil sample, too. Oxidative stability of olive oil samples without and with different levels of UFO (50, 100, 250, 500, 750 and 1000 ppm) and TBHQ (100 ppm) were studied via evaluation of conjugated diene value, carbonyl value, oil/oxidative stability index, acid value and total tocopherol (TT) contents through 8h thermal process at 170°C. Results obtained by oxidative stability assays revealed that the highest antioxidative activity of olive oil was obtained by 100ppm of UFO, followed using 100, 250, 500, 750, and 1000ppm of UFO and 100ppm TBHQ, respectively. Evaluation of the relationship between oxidative stability indexes and TT changes indicated a strong correlation (R2=0.9718) between mean relative resistance to oxidation and relative resistance to TT reduction during thermal process. By promotion of relative resistance to TT reduction, olive oil samples' relative resistance to oxidation was enhanced exponentially; implying importance of TT in promotion of oxidative stability of edible oils. The results obtained in this study showed that UFO has higher antioxidative activity compared to TBHQ; thus UFO can be considered as a natural antioxidant with ideal antioxidative activity.

Effect of Immersed Herbs on the Oxidative Stability of Edible Oils

The improvement of the oxidative stability of edible oils is in the focus of scientific and consumer interest. In the present work the effect of immersion of herbs in edible oils was performed and changes in oxidative stability were measured. Sage and oregano were chosen as herbs and linseed oil, corn germ oil as well as walnut oil as lipid media. Immersion parameters were 3%, 5%, and 7% (w/w) herb/oil, duration: 10 days, temperature: 30°C. Oxidative stability was measured by Rancimat test and FRAP analysis. Results showed that the oxidative stability of the highly sensitive oils -such as linseed and walnut oil- was successfully improved by immersion of herbs. Corn germ oil, which contains a high amount of tocopherols, became similarly more stable, however, only moderately.

1H NMR spectral analysis as a new aspect to evaluate the stability of some edible oils

Oxidative stability is one of the most important indicators for maintaining the quality of edible oils. 1H NMR fingerprinting is used to evaluate the stability of edible oils at room temperature. The assignments of the 1H NMR signals of the major and minor components of unoxidized edible oils and the oil stability prediction were given. Minor components of the oils are playing an essential role in defining oil authenticity and quality. Extra virgin olive oil (EVOO) showed β-sitosterol, whereas, moringa oil (MO) showed β-sitosterol and stigmasterol. MO showed nonglyceride fraction, aliphatic chains and olefins. Sunflower oil (SO) could be easily distinguished due to its high linoleic acid content followed by apricot kernel oil (AKO). The order of stability of edible oils under study was: MO>EVOO>AKO>SO. 1H NMR spectral data agreed with the results obtained from Rancimat method for the determination of oxidative stability of edible oils under study. The main advantages of this method are the short time of analysis, the possibility to analyze samples without any preliminary treatment, and the small quantity of sample required.

Multielemental analysis in vegetable edible oils by inductively coupled plasma mass spectrometry after solubilisation with tetramethylammonium hydroxide

Trace metals have negative effects on the oxidative stability of edible oils and they are important because of possibility for oils characterisation. A single-step procedure for trace elemental analysis of edible oils is presented. To this aim, a solubilisation with tetramethylammonium hydroxide (TMAH) was assayed prior to inductively coupled plasma mass spectrometry detection. Small amounts of TMAH were used, resulting in high elemental concentrations. This method was applied to edible oils commercially available in Argentine. Elements present in small amounts (Cu, Ge, Mn, Mo, Ni, Sb, Sr, Ti, and V) were determined in olive, corn, almond and sunflower oils. The limits of detection were between 0.004μgg−1 for Mn and Sr, and 0.32μgg−1 for Sb. Principal components analysis was used to correlate the content of trace metals with the type of oils. The two first principal components retained 91.6% of the variability of the system. This is a relatively simple and safe procedure, and could be an attractive alternative for quality control, traceability and routine analysis of edible oils.

Near infrared emission photometer for measuring the oxidative stability of edible oils

Near infrared emission spectroscopy (NIRES) allows the determination of the induction time (IT) of edible oils in accelerated oxidation experiments by monitoring the emissivity of a band at 2900nm, which corresponds to the formation of hydroperoxides. In this work, a new near infrared emission photometer dedicated to the determination of oxidative stability is described. The photometer presents several advantages compared to the previously reported NIRES instrument, such as lower cost and extreme simplicity of design and maintenance. The results obtained in the evaluation of the proposed instrument were compared with the official Rancimat method and instrument. The significant advantages include: faster analysis, lower sample consumption and operational simplicity. It is demonstrated that the procedure for determination of oxidative stability of oils can be significantly simplified and performed by measuring the sample emission at only one spectral region centered at 2900nm. Also, the proposed instrument and method present precision equivalent to the Rancimat method (coefficient of variation=5.0%). A significant correlation between the methods has been found (R2=0.81).

Comparison of near‐infrared emission spectroscopy and the Rancimat method for the determination of oxidative stability

AbstractThis work presents a comparison between a new method for the determination of the oxidative stability of edible oils at frying temperatures, based on near‐infrared emission spectroscopy (NIRES), and the Rancimat method at 110 °C. In the NIRES‐based method, the induction time (IT) is determined by means of the variation of the emission band at 2900 nm during heating at 160 °C. The comparison between the IT values obtained with the two methods for 12 samples of edible oils shows some correlation for samples of the same type once there is an agreement on the sequence of highest to lowest IT values between the methods, but a poor correlation considering all samples (correlation coefficient of 0.78). This lack of correlation demonstrates that the results obtained with the Rancimat method cannot be used as an indication of the oxidative stability, or the resistance to degradation, of edible oils at frying temperatures. The difference in the heating temperatures used in the two methods leads to 20–36 times higher IT values for the Rancimat method in relation to the NIRES‐based method, but with similar repeatabilities (2.0 and 2.8%, respectively).

Development of a method predicting the oxidative stability of edible oils using 2,2-diphenyl-1-picrylhydrazyl (DPPH)

The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was used to predict the oxidative stability of edible oils. The principle of DPPH method is to measure the free radicals generated from oxidized oils directly. The absorbance of DPPH from oils before thermal oxidation decreased proportionally to the concentration of free radical scavenging compounds such as butylated hydroxytoluene (BHT). Oxidized oils with high polyunsaturated fatty acid (PUFA) contents showed high changes in DPPH absorbance or free radical formation rates than those with low PUFA. Oxidized oils with high BHT content were more stable and showed slower pattern change of DPPH absorbance from positive to negative slopes than those with low BHT content. Oxidative stability of oils could be predicted considering the initial values of DPPH absorbance, the free radical formation rates, and the oxidation period for pattern changes. The results from DPPH method on the oxidative stability of vegetable oils agreed with conventional methods such as p-anisidine value ( p-AV), conjugated dienoic acids (CDA), or total polar matter (TPM).

Mechanisms and Factors for Edible Oil Oxidation

ABSTRACT: Edible oil is oxidized during processing and storage via autoxidation and photosensitized oxidation, in which triplet oxygen (3O2) and singlet oxygen (1O2) react with the oil, respectively. Autoxidation of oils requires radical forms of acylglycerols, whereas photosensitized oxidation does not require lipid radicals since 1O2 reacts directly with double bonds. Lipid hydroperoxides formed by 3O2 are conjugated dienes, whereas 1O2 produces both conjugated and nonconjugated dienes. The hydroperoxides are decomposed to produce off‐flavor compounds and the oil quality decreases. Autoxidation of oil is accelerated by the presence of free fatty acids, mono‐ and diacylglycerols, metals such as iron, and thermally oxidized compounds. Chlorophylls and phenolic compounds decrease the autoxidation of oil in the dark, and carotenoids, tocopherols, and phospholipids demonstrate both antioxidant and prooxidant activity depending on the oil system. In photosensitized oxidation chlorophyll acts as a photosensitizer for the formation of 1O2; however, carotenoids and tocopherols decrease the oxidation through 1O2 quenching. Temperature, light, oxygen concentration, oil processing, and fatty acid composition also affect the oxidative stability of edible oil.

A new method for determination of the oxidative stability of edible oils at frying temperatures using near infrared emission spectroscopy

This work proposes a new method for determination of the oxidative stability of edible oils at frying temperatures using near infrared emission spectroscopy (NIRES). The method is based on heating an oil sample at a fixed temperature, followed by the acquisition of the emission spectra with time using a home-made spectrometer with an acousto-optical tunable filter (AOTF) as monochromator. The induction time, related to the oxidative stability, is determined by means of the emission band at 2900 nm and its increase and broadening during the heating time. After the induction period, this band also provides information related to the oxidation rate of the sample. Twelve samples of edible oils, of different types and from different manufacturers, were analyzed for oxidative stability with mean repetitivity of 3.7%. The effects of nitrogen insertion, heating temperature and the presence of antioxidant compounds on the oxidative stability were evaluated.

Effect of triacylglycerol structures on the thermal oxidative stability of edible oil

AbstractDifferent molecular species of TAG were assessed to determine the influence of TAG structure on the thermal oxidative stability of edible oil. TAG containing palmitic acid (16∶0, P) as saturated FA (SFA) and oleic acid (18∶1, O), linoleic acid (18∶2, L), or linolenic acid (18∶3, Ln) as unsaturated FA (UFA) were chemically synthesized and then heated at 180 or 150°C. Thermal oxidative stability of TAG was determined by evaluating the resultant UFA, polar compound, FFA, carbonyl compound, polymerized compound, and tocopherol contents. When TAG containing 16∶0 and 18∶2 in the ratio of 2∶1 (mol/mol) were heated at 180°C, a 2∶1 (mol/mol) mixture of saturated TAG (PPP) and unsaturated TAG (LLL) was found to be more susceptible to thermal oxidation than PPP/PLL (1∶1) and PPL. Similarly, a 2∶1 mixture of PPP and OOO or LnLnLn was more unstable toward thermal oxidation than PPO or PPLn, respectively. Thermal oxidative stability of TAG containing SFA and UFA (2∶1) was negatively correlated with the moles of UFA in a single TAG molecule. This tendency was also observed at 150°C. From these results, it is suggested that the TAG structure could be one of the factors determining the thermal oxidative stability of edible oil.

Rapid determination of oxidative stability of edible oils by FTIR spectroscopy using disposable IR cards

AbstractDisposable polytetrafluoroethylene (PTFE) polymer IR (PIR) cards were used as substrates to rapidly oxidize edible oils and simultaneously monitor the extent of oxidation by FTIR spectroscopy. Four edible oils were oxidized on PIR cards and in bulk at moderate temperature (58°C), and real‐time oxidation plots were obtained by measuring changes in the IR hydroperoxide (ROOH) absorbance as a function of time. The relationship between the ROOH absorbance and PV was developed using a reference method to define absorbances corresponding to PV end points of 100 and 200 meq ROOH/kg for the oils oxidized in bulk and on cards, respectively. The real‐time oxidation plots obtained for the oils oxidized in bulk and on cards were similar in appearance, but the oils on the cards reached the PV end point 20 times faster than the oils oxidized in bulk. The results indicate that the use of disposable PIR cards coupled with moderate heating and aeration provides a simple, practical, and rapid means for monitoring oxidation and determining the oxidative stability of edible oils at a normal storage temperature.

Comparative studies of oxidative stability of edible oils by differential scanning calorimetry and oxidative stability index methods

A comparative study was conducted to determine the oxidative stability of twelve different edible oils with two different instruments: a differential scanning calorimeter and an oxidative stability index (OSI) instrument. The OSI instrument temperature was set at 110 °C. The differential scanning calorimetry (DSC) technique involved oxidation of oil samples in an oxygen-flow DSC cell. The DSC cell temperature was set at four different isothermal temperatures: 110, 120, 130 and 140 °C. A dramatic increase of evolved heat was observed with the appearance of a sharp exothermic curve during initiation of the oxidation reaction. The oxidative induction time (T0) was automatically determined by extrapolation of the downward portion of the DSC oxidation curve to the time axis. There was a good correlation (P<0.0001) between the DSC T0 and OSI values. The decrease in log10 (T0) with increasing DSC isothermal temperature was best fitted by a linear equation. DSC evidently provides a convenient way to determine the oxidative stability of various edible oils.

Fourier transform infrared spectra data versus peroxide and anisidine values to determine oxidative stability of edible oils

Different edible oils, including safflower, sunflower, rapeseed and olive oils, were submitted to oxidation in a convection oven with air circulating at 70 °C. Their oxidation process was monitored by Fourier transform infrared spectroscopy by periodically collecting duplicate spectra from films of pure oil between two KBr disks. The frequency and absorbance of each infrared band were automatically registered by a macro program. Classic chemical methods for determining primary and secondary oxidation products, such as peroxide value and anisidine value respectively, were determined periodically. Changes observed in infrared data are useful indicators of edible oils oxidative stability and are closely related to changes observed in peroxide and anisidine values in the course of the oxidation of the samples. Fourier transform infrared spectroscopy may be able to substitute classic oxidation indices in the determination of oxidative stability or antioxidant activity due to its simplicity, low cost and time saving.

Usefulness of the frequency data of the fourier transform infrared spectra to evaluate the degree of oxidation of edible oils.

The oxidation process of 13 edible oil samples with different proportions of oleic, linoleic, and linolenic acyl groups has been studied using Fourier transform infrared spectroscopy. The oxidation experiments were carried out by heating the samples in a convection oven at 70 degrees C. Duplicate spectra were recorded from a film of pure oil between two disks of KBr for each sample every day during the course of the oxidation, and frequency data of each band of the spectrum were collected automatically. Changes in the values of the frequency of most of the bands of the spectra were observed. The shiftings of the frequency value of specific bands allowed one to distinguish between the different stages of the oxidation process and to establish the oxidation degree of each oil sample. This methodology could be useful to evaluate the oxidative stability of edible oils in a simple, fast, and accurate way.

Assessment of thin‐film oxidation with ultraviolet irradiation for predicting the oxidative stability of edible oils

AbstractThe oxidative stability of edible oils and samples of rapeseed oil with added antioxidants, metal ions, phospholipids and oxidized oil was assessed by a method involving oxidation of a thin film of oil with ultraviolet (UV) irradiation at 100°C. Induction times determined by this method were compared with those determined with the Rancimat at 100°C. The two methods agreed well in describing the effects of additives on the stability of the edible oil. Induction times were considerably shorter for the thin‐film UV method, and the method may have potential as an accelerated test method for assessing the effect of additives on the oxidative stability of relatively stable oils and fats. The correlation between the Rancimat and the thin‐film UV induction times also was assessed at 80°C for rapeseed oil containing additives, but there was no advantage in using the lower temperature alone because the induction times were 2–7 times longer than at 100°C. However, use of two elevated temperatures is likely to improve predictions of stability at lower temperatures, especially for samples containing copper, which have an exceptionally high‐temperature coefficient. The thin‐film UV method showed a poorer agreement with the Rancimat for comparing the oxidative stability of some fats and oils. For instance, corn oil was more stable than soybean oil in the Rancimat test but the order of stability was reversed in the thin‐film UV test. Cocoa butter was much more stable in the Rancimat test than when assessed by the thin‐film UV test.